Weight loss is a frequently recommended treatment for obese patients with obstructive sleep apnea (OSA). The empirical support for this recommendation is lacking. Based on descriptive studies, weight loss appears to improve but not abolish sleep disordered breathing. Moreover, the degree of improvement in OSA is quite variable and not directly proportional to weight loss. The lack of randomized trials, the study of predominantly male samples, and the absence of follow-up evaluations leave physicians and patients unsure about the utility of weight loss treatment in obese OSA patients. The research proposed in this application will assess the effects of weight loss on sleep disordered breathing in 120 obese, Type 2 diabetics with OSA (RDI greater than or equal to 15) who are randomly assigned to either weight loss (n=60) or usual care (n=60) treatments within the context of the Look AHEAD study. Home polysomnography studies will be performed before treatment and at 1 and 2 years. Among the 60 weight loss subjects, we will assess the relative importance of changes in neck and abdominal fat in explaining the variability of changes in sleep disordered breathing after weight loss. Finally, we will examine the relationship between changes in sleep-disordered breathing and changes in blood pressure after weight loss in the 60 weight loss participants. Specifically, this research will: 1) determine the efficacy of a weight loss program in reducing sleep disordered breathing in obese Type 2 diabetics; 2) identify sources of variability in sleep disordered breathing associated with weight loss; and 3) examine the role of sleep disordered breathing in mediating changes in blood pressure associated with weight loss. The results of this study will provide an empirical basis for making recommendations about the effectiveness of weight loss in Type 2 diabetics with OSA.